A water-treatment process used to eradicate harmful bacteria and viruses by exposing potentially contaminated water to ultraviolet radiation. At a certain level of intensity, ultraviolet light is fatal to all microorganisms that inhabit water. Mercury arc lamps are used to generate the ultraviolet radiation with low-pressure lamps being the most common and effective. The lamp is made of fused silica or quartz to allow transmission of the ultraviolet light. The efficiency of UV disinfection is diminished by turbidity and by the build-up of scale on the tubes.